1. Field of the Invention
The present invention relates to a wireless transmission apparatus, a wireless reception apparatus, a wireless communication system, and a wireless communication method that are applicable to a millimeter-wave transmission system for fast transmitting signals of millimeter band in which carrier frequencies for carrying movie images, computer images, and the like are 30 GHz to 300 GHz in the housing of each apparatus.
2. Description of the Related Art
As the volumes of information such as movie images, computer images and the like have been enormously growing in the recent years, the demands for high-speed and mass-capacity digital communication, irrespective of wired or wireless, have been constantly increasing. In such high-speed, mass-capacity digital communication, use of apparatuses for transmitting modulated signals of millimeter waves for example at high speeds has been growing. The high-speed signal transmission apparatuses of this kind are desired to transmit high-speed modulated signals of millimeter wave for example to the reception side without involving errors.
A wireless communication system for transmitting high-speed wireless modulated signals of millimeter wave is made up of a wireless transmission apparatus and a wireless reception apparatus, for example. The wireless transmission apparatus has a transmission baseband processing block and a wireless transmission block. The transmission baseband processing block processes a digital signal entered from an upper digital data processing block to generate a baseband signal. The wireless transmission block has a local oscillator superimposes the baseband signal generated by the transmission baseband processing block with the local oscillation signal generated by the local oscillator to generate a wireless modulated signal.
The wireless reception apparatus has a wireless reception block and a received baseband processing block. The wireless reception block has a local oscillator and superimposes a wireless modulated signal received from the transmission side with a local oscillation signal outputted from the local oscillator to generate a baseband signal. The received baseband processing block outputs a digital signal obtained by processing the baseband signal entered from the wireless reception block to an upper digital data processing block. Consequently, large volumes of digital signals can be communicated from the transmission side to the reception side at high speeds.
The local oscillation frequency of a local oscillation signal of each of the wireless transmission apparatus and the wireless reception apparatus is generated by a voltage controlled oscillator (VCO) for example inside each apparatus. This configuration disables both the transmission side and the reception side to generate a local oscillation signal having the exactly the same local oscillation frequency. Therefore, a difference is caused in the local oscillation frequency of each local oscillation signal between the wireless transmission apparatus and the wireless reception apparatus. In order to solve this problem, a local oscillator excellent in frequency stability and low in phase noise is desired. In addition, in order to correct the difference between the local oscillation frequencies, a PLL (Phase Locked Loop) circuit is used.
There is an injection locking method in which the local oscillation frequency of a local oscillation signal is equally pulled in at the transmission side and the reception side mentioned above. This injection locking technique, long known, injects the local oscillation signal having a local oscillation frequency from the wireless transmission apparatus into the wireless reception apparatus, thereby providing the local oscillation frequency locking between the transmission side and the reception side.
For communication apparatuses for transmitting and receiving millimeter waves of this kind, “A Study of Locking Phenomena in Oscillators” (1), ROBERT ADLER, A paper reprinted from the June 1946 issue of the PROCEEDINGS OF THE IRE (hereinafter referred to as Non-patent document 1) and “A Study of Injection Locking and Pulling-in Oscillators” (2), Behzad Razavi, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 39, NO. 9, SEPTEMBER 2004 (hereinafter referred to as Non-patent document 2) disclose new injection locking methods based on the multiple locking of a millimeter-wave solid oscillator. This millimeter-wave solid-state oscillator has a DC bias circuit, a coaxial circuit, and an oscillator and uses multiple locking for injection locking. In the multiple locking, a signal that is an integral submultiple of the main oscillation frequency is externally injected to stabilize an oscillation wave.
In doing so, a DRS (DC bias RF Separate) circuit is used. In DRS, an injection signal is supplied to an oscillator from a coaxial circuit separate from a DC bias circuit and this injection signal is coupled with the electromagnetic field generated around an oscillation element. Configuring the millimeter-wave solid-state oscillator as described above can inject a stable signal into the oscillator and simplify the injection circuit.
With respect to a wireless communication system based on the injection locking of this type, Japanese Patent Laid-open No. 2001-053640 (page 4, FIG. 2) (hereinafter referred to as Patent document 1) discloses a wireless communication apparatus and a wireless communication method. This wireless communication apparatus has a wireless transmitter and a wireless receiver. The wireless receiver has a band filter and an injection-locking type oscillator. In down-converting a wirelessly transmitted signal into an intermediate frequency band on the reception side, the wireless transmitter modulates the input signal into an intermediate frequency band and up-converts a resultant intermediate frequency band modulated signal into a wireless frequency band. The wireless transmitter wirelessly transmits a local oscillation signal used in the up-conversion to the reception side along with the wireless frequency band modulated signal.
The wireless receiver receives a wireless reception signal made up of the local oscillation signal and the wireless frequency band modulated signal from the wireless transmitter and generates a multiplication component obtained by multiplying the local oscillation signal component by the wireless frequency band modulated signal component. By this generation of the multiplication component, the wireless receiver down-converts the reception signal into an intermediate frequency band to demodulate an intermediate frequency band modulated signal obtained by this down conversion.
Upon completion of the above-mentioned processing, the band filter extracts a non-modulated carrier signal (or a local oscillation signal) from the wireless reception signal (or the composite signal) made up of the local oscillation signal and the wireless frequency band modulated signal. The injection-locking type oscillator is arranged so as to reproduce the non-modulated carrier signal extracted by the band filter. Configuring the wireless communication apparatus as described allows the installation of the same local oscillator as the local oscillator installed on the transmitter, so that the configuration of the receiver can be simplified and the manufacturing cost of the receiver can be lowered.
Japanese Patent Laid-open No. 2003-244016 (page 4, FIG. 1) (hereinafter referred to as Patent document 2) discloses a wireless communication method and a wireless communication system that execute communication between two or more wireless communication terminals. This wireless communication system has one transmission station and two or more wireless communication terminals. Each of the wireless communication terminals has an injection locking oscillator, a transmission functional block, and a reception functional block. The transmission functional block multiplies an intermediate frequency band modulated signal by a local oscillation signal to generate a wireless modulated signal. The reception functional block multiplies the wireless modulated signal by the local oscillation signal to generate a down-converted intermediate frequency band signal.
Upon completion of the above-mentioned processing, the transmission station transmits only a reference local oscillation signal to each wireless communication terminal. Each of the two or more wireless communication terminals receives the reference local oscillation signal radiated from the transmission station. Each wireless communication terminal amplifies and band-filters the received reference local oscillation signal and then reproduces the reference local oscillation signal by the injection locking oscillator. Each wireless communication terminal sets the reference local oscillation signal as a local oscillation signal for use by the transmission function block and the reception functional block and executes communication between the wireless communication terminals by use of this local oscillation signal.
Configuring the system as described above allows the solution of the signal degradation caused by the local oscillation signal used to provide the effective use of frequency and, at the same time, allows the provision of a wireless communication system that supposes N-to-N communication configured by N terminals.